Field of the Invention
The present invention relates to an electroconductive member that charges a member to be charged by discharge, in particular, an electroconductive member that can be utilized as a charging member, a transfer member or the like for use in an electrophotographic apparatus, as well as a process cartridge and an electrophotographic apparatus using the same.
Description of the Related Art
An electroconductive member that charges a member to be charged by discharge is used for an electrophotographic apparatus, an ozone generation apparatus, a neutralization apparatus, an air cleaner, an electrostatic dust collector, an electrostatic coating apparatus, an electrostatic adsorption apparatus or the like. In particular, in the electrophotographic apparatus, for example, an electroconductive member such as a charging member or a transfer member is used.
In the electrophotographic apparatus, the electroconductive member is disposed in contact with or close to a recording medium including an electrophotographic photosensitive member or a dielectric member that serves as the member to be charged, and the surface of such a member to be charged is subjected to a charging treatment by discharge due to application of a direct voltage obtained by superimposing an alternate voltage or only a direct voltage.
With an increase in speed of an electrophotographic image forming process, a time spent for charging the member to be charged has been relatively shorter in recent years. Such a trend is disadvantageous for stably and certainly charging the member to be charged. Specifically, the increase in speed of an electrophotographic image forming process makes it difficult to impart a sufficient charge potential to the surface of the member to be charged. In view of such a problem, Japanese Patent Application Laid-Open No. 2005-316263 discloses a technique in which the outermost layer of a charging member contains a ferroelectric particle to result in an increase in dielectric constant, thereby leading to an increase in amount of a discharge current.
In addition, Japanese Patent Application Laid-Open No. 2004-245933 discloses a technique in which at least one layer located below the surface layer of a multi-layer charging member is a layer high in electric resistance to thereby result in an improvement in charge performance.
According to studies by the present inventors, a voltage applied to the electroconductive member is required to be increased in order to impart a sufficient charge potential to the member to be charged in the electrophotographic image forming process having an increased speed. When the voltage applied is increased in the charging member disclosed in each of Japanese Patent Application Laid-Open No. 2005-316263 and Japanese Patent Application Laid-Open No. 2004-245933, however, a local and strong discharge (hereinafter, also referred to as “abnormal discharge”) may be induced to prevent a stable discharge and to cause an image unevenness in a range from several tens of micrometers to several millimeters due to the abnormal discharge.